One of the biggest concerns we hear from parents is about their child's thumb sucking habit. Our advice: if they're under age 4, there's no need for concern — yet. If they're older, though, you should be concerned about the possible effect on their bite.

Thumb sucking is a universal habit among infants and toddlers and is related to their swallowing pattern during feeding. As they swallow, their tongue thrusts forward to create a seal with the lips around the breast or a bottle nipple. Many pediatricians believe thumb sucking replicates nursing and so has a comforting effect on infants.

Around age 4, though, this swallowing pattern begins to change to accommodate solid food. The tongue now begins to rest at the back of the top front teeth during swallowing (try swallowing now and you'll see). For most children, their thumb sucking habit also fades during this time and eventually stops.

But for whatever reason, some children don't stop. As the habit persists, the tongue continues to thrust forward rather than toward the back of the top front teeth. Over time this can place undue pressure on both upper and lower front teeth and contribute to the development of an open bite, a slight gap between the upper and lower teeth when the jaws are shut.

While late childhood thumb sucking isn't the only cause for an open bite (abnormal bone growth in one jaw is another), the habit is still a prominent factor. That's why it's important that you start encouraging your child to stop thumb sucking around age 3 and no later than 4. This is best accomplished with positive reinforcement like rewards or praise.

If they've continued the habit a few years after they should have stopped, we may also need to check to see if their swallowing mechanism has become stunted. If so, we may need to use certain exercises to retrain their tongue to take the proper position during swallowing.

While you shouldn't panic, it's important to take action to stop thumb sucking before it becomes a long-term problem. A positive, proactive approach will help avoid costly orthodontic problems later in their lives.